I have a bike ride on each end of my train ride and it's really not so bad. Okay, maybe not the perfect situation, but quite live-able. I usually fold my bike before getting on the train and stay in one of the standing sections, which I find more comfortable than sitting in (sometimes) sweaty clothes.
Plus, as Lalato pointed out, if you just ride a bit slower you won't get sweaty, or at least not nearly so much. For me, the commute in the morning is cool or cold, the ride home is either warm or hot weather, so I just cruise in the AM and hammer (if I'm feeling up to it) in the afternoon.
The cycling part of my commute (round trip) is just a tad over 24 KM.
Rick / OCRR